In recent years, it has become practical to use a high-speed cellular radio communication technique, such as LTE (Long Term Evolution), WiMAX, etc., and therefore, the communication rate of radio communications services enjoyable for mobile users has been significantly improved. Moreover, it is expected that the introduction of the fourth-generation cellular radio communication technique, such as LTE-A (LTE-Advanced) etc., would further improve the communication rate.
On the other hand, there has been a rapidly increasing number of mobile users, and therefore, there has been increasing use of applications requiring a high data rate. As a result, the cellular radio communication technique has not yet been developed to meet all needs of mobile users. Therefore, a small cell is beginning to be introduced in order to supplement a macro cell and thereby increase communication capacity. The concept of a small cell encompasses a femtocell, a nanocell, a picocell, a microcell, etc. A small cell is typically introduced by providing a base station (also called an access point) which is smaller than that (e.g., an eNB (evolved Node B) in LTE) of a macro cell. However, in an area where a macro cell and a small cell overlap, there is a risk that a radio signal communicated in the small cell may interfere with a terminal connected to the macro cell.
As a technique for avoiding the risk of interference in the cellular radio communication system, a technique proposed by Patent Literature 1 below is known, for example. According to the technique proposed by Patent Literature 1 below, interference channel information is exchanged between adjacent macro cell base stations, and based on the exchanged interference channel information, transmission power is adjusted by these base stations.